System, method and apparatus for entraining air in concrete

ABSTRACT

A method of preparing a concrete composition for downhole injection includes utilizing a controller to control a process including circulating process water in a process water supply loop for a predetermined period while monitoring and controlling the temperature and flow rate of the process water, circulating aqueous-based air entrainment solution in an aqueous-based air entrainment solution supply loop for the predetermined period and controlling the flow rate of the aqueous-based air entrainment solution and after the predetermined period of time in which the flow of process water and aqueous-based air entrainment solution have stabilized, simultaneously actuating valves to divert and mix the process water, the aqueous-based air entrainment solution and compressed air to produce an air-entrained foam and mixing the foam with a concrete composition to be deployed downhole.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/748,883, filed on Mar. 29, 2010, entitled “SYSTEM, METHOD ANDAPPARATUS FOR ENTRAINING AIR IN CONCRETE,” published on Sep. 30, 2010under publication No. US 2010/0246312, the specification of which isincorporated herein by reference for all purposes, and which is acontinuation-in-part of U.S. patent application Ser. No. 11/709,932,filed on Feb. 21, 2007, entitled “METHOD AND APPARATUS FOR MAKINGAIR-ENTRAINED OR CELLULAR HIGH-STRENGTH CONCRETE,” published on Feb. 7,2008 under publication No. US 2008/0028988, the specification of whichis incorporated herein by reference for all purposes.

U.S. patent application Ser. No. 11/709,932 claims the benefit of U.S.Provisional Application for Patent Ser. No. 60/775,571, filed on Feb.21, 2006, and entitled “METHOD AND APPARATUS FOR MAKING AIR-ENTRAINED ORCELLULAR HIGH-STRENGTH CONCRETE,” the specification of which isincorporated herein by reference for all purposes.

TECHNICAL FIELD

A system, method and apparatus for entraining air in concrete fordownhole injection is disclosed. In particular, a system and methodutilizing an aqueous-based air entrainment solution foam to incorporateair in concrete as the cement slurry is prepared for a downholecementing and/or the concrete is batched is set forth.

BACKGROUND

It is desirable to entrain air in concrete for a variety of reasons. Forexample, when concrete is to be exposed to moisture, deicers andfreeze/thaw temperature cycles, it is necessary to entrain air in theconcrete to avoid cracking and crumbling due to hydraulic pressuresproduced in the pores and capillaries of the concrete as the moisturefreezes. The use of entrained air may also reduce the amount of cementrequired, reducing the cost of the mix. However, in the case of moderateto high strength concrete, each percent of entrained air (volume basis)will reduce the compressive strength of the cured concrete. Thisreduction in compressive strength will vary with the particular concreteblend, the physical and chemical properties of the blend components,e.g., cement, sand, rock, admixtures etc. Further, currently usedair-entrainment admixtures and systems do not provide the desired degreeof consistency and repeatability in terms of the volume of air-entrainedin concrete. This, in turn requires recalibration of the amount ofadmixtures added to the concrete and the use of additional cement in theblend to ensure that the resulting product meets the requiredspecifications for the particular application.

Also, the air-entrained cementing (lightweight cementing) with itsparticular type known also as “foamed cementing” or “cellular cementing”has been utilized in a wellbore cementing to reduce the density of thecement column thereby reducing the hydrostatic pressure of the cementslurry column on the rock formations. Simply, lightweight cements aredesirable because they will exert less hydrostatic pressure on the rockformation. If the formation fractures during the cementing process, thecement will enter the formation and compromise the ability to placecement along the entire wellbore; this, ultimately, causes a poor orfailed cementing of the wellbore. The lightweight cement is ofparticular usefulness in weak formations, i.e. in formations havingrelatively low fracture gradient. Foamed cement has several advantagesin addition to its low density. It has relatively high compressivestrength (which is developed in a reasonable time), causes less damageto water-sensitive formations, can reduce the chance of annular gasflow, and allows cementing past zones experiencing total losses.

Cementing of the wellbore is performed when the cement slurry isdeployed into the well via pumps. The cement slurry displaces thedrilling fluids remaining within the well, and replaces the fluids withcement. Preferably, such displacement should be performed in acontinuous manner such that there is no interruption to the flow ofcement. Such process requires a continuous delivery of a desired qualityand quantity of cement slurry so that the first cement down the holeremains stable until last cement is placed after one continuousoperation. Then, the cement must remain stable while it is static up anduntil the time it sets or hardens. This can take up to 4-6 hours toplace cement and up to 12 hours for the cement to set uphole where thetemperatures are cooler than the bottom of the well. The cement slurryflows to the bottom of the wellbore through the casing. From there, itfills in the annular space between the casing and the wellbore, andhardens or sets. The hardened cement creates a seal so that outsidematerials (including gases) cannot enter the well flow, as well aspermanently positioning and protecting the casing in place.

Downhole cementing poses particular problems caused by changingtemperatures and hydrostatic pressure along the cement column, thusmaking conventional cement preparation and composition practicallyunsuitable for a downhole cementing.

Preparing slurry having the required physical properties is essentialbefore commencing cementing operations. The proper cement chemistry mustbe determined, and the mix prepared to provide slurry having therequired density and viscosity before the slurry is pumped into thehole. Special mixers, including hydraulic jet mixers, re-circulatingmixers or batch mixers, are used to combine dry cement with water tocreate the wet cement. The cement used in the well cementing process isPortland cement, and it is typically prepared with additives to form oneof a number of different API classes of cement. Each is employed forvarious situations. Additives can include accelerators, which shortenthe setting time required for the cement, as well as retarders, which dothe opposite and make the cement setting time longer. In order todecrease or increase the density of the cement, lightweight andheavyweight additives are added. Additives can be added to transform thecompressive strength of the cement, as well as flow properties anddehydration rates. Extenders can be used to expand the cement in aneffort to reduce the cost of cementing, and antifoam additives can beadded to prevent foaming within the well. In order to plug lostcirculation zones, bridging materials are added, as well.

Depending upon the particular formation, bore depth equipment and otherfactors, it may be necessary or desirable to mix additives with thecement to retard setting, accelerate setting time, control fluid loss inthe cement, gel the cement and reduce or increase the slurry density.Additives may be used to increase the mechanical strength of the cementwhen set, reduce the effect of mud on the cement and to improve thecement bonding. Additives are typically mixed with the cement as theslurry is prepared and before the cement is pumped into the well. Insome cases, there may be different pozzolanic materials combined withthe cement itself but, as noted above, typically Portland cement isblended with additives and/or modified to accommodate wellboreconditions such as temperatures up to or greater than 600 degreesFahrenheit. In different variations, binders other than Portland cementmay be used, for example, fly ash and other pozzolanic materials.

The physical characteristics of Portland cement and similar binders maytend to create a drag effect, affecting the flow characteristics of thecement. In particular, Portland cement particles have a generally flatshape that creates a drag effect, reducing the flowability of thecement. Adding components such as fly ash in combination with Portlandcement can alleviate some of this drag effect, but the addition of flyash may create other issues such as variability in the heat of hydrationof the cement and/or the set time of the cement. Variability in thephysical and chemical properties of fly ash utilized as an additive inoilfield cement can also increase variability in the chemistry andphysical properties of the slurry. Such variability may be small;however, in well cementing applications, the effect of such variabilitycan be significant.

Water is of course, necessary to hydrate the Portland cement and provideappropriate flow properties. However, if excessive water is used,separation of the water from the cement mixture may occur, especiallyonce the cement stops flowing. Excessive water may also cause loss ofstrength, excessive shrinkage and variability in hydraulic pressure,which may be detrimental in different applications. Fluid loss additivesmay be used to reduce a segregation and separation of wellbore cementcomponents and compensate for water imbalance. Fluid loss additives aredesigned to keep the cement slurry more cohesive over a range of commonvariables and to mitigate the effect of excessive water in the slurry.However, the increased cohesiveness of the slurry tends to reduce theflow rate of the cement slurry into the bore. One way of improving theflow properties of the cement slurry and/or compensating for the effectof fluid loss products, is to entrain air into the slurry as or beforethe slurry is injected into the bore.

During the manufacturing of the foamed cement, conventional airentrainment techniques typically use surfactant formulations which arelargely or totally anionic based compositions added to cement slurries.Methods using these compositions are practically unable to compensatefor large changes in cement and/or pozzolanic chemistry, agitationconditions, slurry temperatures and other factors that change thecharacteristics of the slurry. Variations in these parameters limit thecapability to predict or calculate slurry yield volume and/or thequality of the air entrainment in the slurry injected into the well.Unstable slurries result in a pore structure which is nonspherical andinterconnected. This phenomenon occurs while the cement sets. It iscaused by a rupture of unstable nitrogen bubble walls (conventional foamcementing usually utilizes disperse gases such as nitrogen) upon contactwith other nitrogen bubbles, resulting in coalescence and larger gaspockets. This results in a sponge-like structure with lower compressivestrength, higher permeability, and inferior bonding properties. Thisinability to control sources of variability and/or to compensate for theeffects of these sources of variability limits the desirability ofutilizing air entrainment (foamed gas) as a method of adjusting slurryparameters or limiting the amount of cement used in the slurry fordownhole injection.

It is possible to find a single gas-to-base slurry ratio (a “constantgas ratio”), which satisfies the boundary condition (density of the leadslurry, fracture pressure profile, pore pressure profile, formationpermeability) of usually shallower formations. Operationally, this isthe simplest method, because the gas injection (air or nitrogen) rateremains constant during the cement job. This method results in avariable foam quality throughout the cement column, with a low densityat the top, and the constantly increasing density with depth because ofhydrostatic compression of the well bore. However, due to a variablehydrostatic pressure and temperatures in a wellbore environment, thereis a need to produce cement slurry of variable density to account for achanging hydrostatic pressure in a wellbore column. These real timeadjustments in a density of the cement slurry pose a challenge whichprior art has yet to solve, for it requires complex pumping schedulewith close coordination and control of the treatment on location.

Accordingly, there is a need for safer and more cost-effective downholecementing system and method that manufactures lightweight, cellularcement in a continuous or a batch process. There is also a need forproducing stable and homogeneous cement slurry for a downhole cementingof a wellbore having physical and chemical characteristic which preservecompressive strength at high temperature. There is also further need forwell cementing that increases productivity of the well by avoiding thedowntime caused by abandoning the well in case of a poor/inadequatecementing job. Thus, there is a need for producing stable, cellularcement slurry with predictable chemical and physical characteristicswhich assures longevity and safer operation of a producing well. Simply,it is desirable to produce stable cement slurry having air entrainedcomponent for a downhole cementing.

SUMMARY

A system for preparing a concrete composition including entrained airfor downhole injection includes a controller for controlling the system,the controller having one or more communications interfaces forcommunicating with system components such as instruments, sensors,meters, position indicators and for transmitting control signals. Thecontroller may be operable to compare signals received from variousinstruments such as flow, temperature and pressure sensors, compare thesignals to preprogrammed values and make process adjustments when thevalues vary from the preprogrammed values. For example, the controllermay be operable to adjust the speed of a pump to control a flow rate. Adata storage device associated with the controller may be used forstoring predetermined process parameters such as flow rates, pressuresand temperatures and for storing historical data.

In one embodiment, the system includes a process water supply circuitfor providing temperature controlled process water to produceair-entrained foam. The process water supply circuit may include aprocess water supply tank having a temperature monitoring device and alevel detecting device. The temperature monitoring device and leveldetecting device provide signals to the controller indicating the levelof process water in the water supply tank and the temperature of theprocess water in the process water supply tank. In one variation, aclosed loop circulating system is used to control the temperature of thewater in the process water supply tank. As dictated by environmentalrequirements, a closed loop circulation system includes a circulatingpump, water heater and/or refrigeration system. The circulating pumppumps water from the process supply tank through the water heater whenthe water is below set point or passes through the cooling system whenthe water is above set point, then it goes back into the process tank.The closed loop circulating system is controlled by the controller whichreceives a signal from the temperature monitor which energizes thecirculation pump as well as the heating or cooling device respectively.

The process water supply circuit further includes a process watercirculating loop including a process water supply pump that pumps waterfrom the process water supply tank through the process water circulatingloop and back to the process water supply tank. The process water supplypump is driven by a first variable speed drive under the control of thecontroller which may compare a signal from a flow meter in the processwater circulating loop to a preprogrammed set point and adjust the speedof the drive if the flow varies from the set point. A first valve in theprocess water circulating loop may be actuated by the controller todivert process water from the process water circulating loop to produceair-entrained foam.

The system further comprises an aqueous-based air entrainment solutionsupply circuit for providing an aqueous-based air entrainment solutionfor producing air-entrained foam. In one embodiment, the aqueous-basedbased air entrainment solution is a polymer-based solution. Thepolymer-based solution supply circuit may include a polymer-basedsolution batch tank having a polymer-based solution level detectingdevice for monitoring the level of polymer-based solution in the batchtank. The polymer-based solution level detecting device transmits asignal to the controller that indicates the level of polymer-basedsolution in the tank. The controller may add polymer-based solution tothe batch tank by pumping additional polymer-based solution from a bulktank and/or annunciate an alarm to notify an operator of a low levelcondition in the tank.

The polymer-based solution supply circuit further includes apolymer-based solution circulating loop with a polymer-based solutionsupply pump for pumping polymer-based solution from the polymer-basedsolution batch tank through the polymer-based solution circulating loopand back to the polymer-based solution batch tank. The polymer-basedsolution supply pump may be driven with a second variable speed driveunder the control of the controller. A flow meter in the polymer-basedsolution supply circuit transmits a signal to the controller whichcompares the flow rate to a preprogrammed set point and adjusts thespeed of the drive to correct the flow rate as necessary. The controllermay also annunciate an alarm if the polymer-based solution flow ratevaries from the preprogrammed set point. The controller may reposition asecond valve in the polymer-based solution circulating loop to mix withthe process water to produce an air-entrained foam.

A compressed air supply may include a particulate filter for removingparticulates from the air and a dryer for drying the compressed air.Compressed air is supplied to the system through a pressure regulatorand an air supply valve operating under the control of the controller.

In operation, process water and polymer-based solution are circulatedthrough their respective circulating loops for a predetermined period tostabilize the flows and the process water temperature before the firstand second valves are actuated to divert process water and polymer-basedsolution to a mixing chamber. Compressed air is added to the blendedprocess water and polymer-based solution down stream of the mixingchamber where compressed air is added to the stream. The stream ofprocess water, polymer-based solution and compressed air is directedthrough a stationary mixer to produce an air-entrained foam. Theair-entrained foam is discharged through a discharge line for mixingwith a concrete composition to form an air-entrained concrete, andfurther deployed into the wellbore to set in a cement column havingconstant density.

According to one embodiment of the present disclosure, the systemdescribed herein is capable of producing a single gas-to-base slurryratio (a “constant gas ratio”).

In one embodiment, the system also includes a pressure sensor in thedischarge line that transmits a signal to the controller. The controlleris operative to actuate an alarm when the signal from the pressuresensor indicates a variance in one of the flow of process water, theflow of the polymer-based solution or a change in the pressure of thecompressed air used to produce the air-entrained foam.

In one embodiment, a process for preparing a concrete compositionincluding entrained air for downhole injection includes circulatingwater and polymer-based solution in closed circuits for a predeterminedperiod before mixing to allow process parameters to stabilize beforeproducing air-entrained foam. Accordingly, the process includescirculating process water in a process water supply circuit for apredetermined period while monitoring the flow rate of the process waterin the water supply circuit with a flow meter and transmitting a flowrate signal to a controller. The flow rate of the process water iscompared to a preprogrammed process water flow rate range with thecontroller. If the flow rate is outside of the preprogrammed range, thecontroller transmits a signal to, for example, a variable speed pumpdrive, to adjust the flow rate of the process water. The temperature ofthe process water is also monitored with a temperature sensor whichtransmits the temperature to the controller which compares the processwater temperature to a preprogrammed process water temperature range. Ifthe temperature of the process water falls below the preprogrammedprocess water temperature range, the controller transmits a signal to aheating device to adjust the temperature of the process water.

In one aspect, polymer-based solution is circulated in a polymer-basedsolution supply circuit during the predetermined period while monitoringthe flow rate of the polymer-based solution in the polymer-basedsolution supply circuit with a flow meter. The flow meter transmits asignal to the controller which compares the flow rate of thepolymer-based solution in the polymer-based solution supply circuit to apreprogrammed polymer-based solution flow rate range and transmits asignal to adjust the polymer-based solution flow rate if thepolymer-based solution flow rate is outside of the programmed range. Thepressure of a compressed air supply used to produce the air-entrainedfoam is also monitored with a pressure sensor which transmits thepressure to the controller which in turn compares the pressure of thecompressed air supply to a preprogrammed air pressure range.

After the predetermined period, if the process parameters are stabilizedwithin the preprogrammed ranges, the process water flow rate is withinthe preprogrammed process water flow rate and the process watertemperature is within the preprogrammed process water temperature rangeand the polymer-based solution flow rate is within the preprogrammedpolymer-based solution flow range, then process water from the watersupply circuit and polymer-based solution from the polymer-basedsolution supply circuit are simultaneously, or substantiallysimultaneously diverted to a first mixer. Compressed air is added to themixed process water and polymer-based solution to produce air-entrainedfoam. In one embodiment, the process water, polymer-based solution andcompressed air are directed to a second mixer for additional mixing. Theair-entrained foam is directed to a discharge line and discharged into awet or dry concrete composition to produce a cement compositionincluding entrained or captured air.

In one aspect, the process includes receiving an order for a specifiedamount of air-entrained foam for a batch of concrete with thecontroller. The order may be electronically transmitted to thecontroller or manually entered with a local or remote user interface.The controller may then calculate a run time to produce the specifiedamount of air-entrained foam. The specified amount of air-entrained foamis produced under the control of the controller and discharged into aconcrete batch and further deployed downhole. As the foam is producedand discharged, the pressure in the foam discharge line may be monitoredand transmitted to the controller which compares the pressure to apreprogrammed pressure range. If the pressure in the discharge linevaries from the preprogrammed range, the controller may initiate apreprogrammed set action such as annunciating a local or remote alarmand/or transmitting a signal to a remote central office indicating thatthe pressure in the discharge line has varied from the preprogrammedrange. After the specified amount or volume of air-entrained foam isproduced, any foam remaining in the discharge line may be purged withone or more pulses of compressed air to clear the line.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding, reference is now made to thefollowing description taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is a schematic representation of a system utilized to produce apolymer-based foam for air entrainment in downhole injection.

FIG. 2 is a diagrammatic representation of one variation of a system forproducing a polymer-based solution foam for entraining air in concrete;

FIG. 2A is a simplified diagrammatic representation of the generalcontrol system;

FIG. 3A is a diagrammatic representation of the system of FIGS. 1 and 2;

FIG. 3B is a diagrammatic representation of the system of FIGS. 1 and 2,illustrating one configuration of control paths;

FIGS. 4A-4C is a flow chart illustrating an exemplary process using thesystem of FIGS. 1 and 2 to provide polymer-based solution foam forentraining air into concrete;

FIG. 5 illustrates a detail of the process flow as illustrated in FIG.2A;

FIG. 6 illustrates a process flow for running integrated andnon-integrated process flows; and

FIG. 7 illustrates a flow chart for the operation of the sub processwhen changing over from the non-integrated mode to the integrated mode.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numbers are usedherein to designate like elements throughout, the various views andembodiments of a system, method and apparatus for entraining air inconcrete for downhole injection are illustrated and described, and otherpossible embodiments are described. The figures are not necessarilydrawn to scale, and in some instances the drawings have been exaggeratedand/or simplified in places for illustrative purposes only. One ofordinary skill in the art will appreciate the many possible applicationsand variations based on the following examples of possible embodiments.

FIG. 1 is a schematic representation of a concrete batch plant 10, oftenreferred to as a ready-mix plant. A typical batch plant 10 may beprovided with a number of silos or hoppers 12 for storing cement, sand,rock and other aggregates or material such as fly ash. Predeterminedamounts of the different materials are discharged from silos 12 throughgates 14 and chutes 16 into the rotating drum 18 of a concrete truck 20.Typically, control of the amounts of the various materials included in abatch is accomplished by opening gates 14 for predetermined time periodsto discharge the desired volume of the materials.

Concrete batch plant 10 may be either a dry batch plant or a wet batchplant. In the case of a dry batch plant, the dry materials, e.g.,cement, sand, stone, and other components, are loaded into truck 20 in adry state and water is added thereafter. The dry materials and the waterare mixed with the dry components by rotation of drum 18 of truck 20 enroute to the job site. In the case of a wet batch plant, the drycomponents and water are mixed prior to the concrete being loaded in thetruck.

In one embodiment, a system 200 is used in conjunction with concretebatch plant 10 to produce a concrete composition with entrained air fordownhole injection. As used herein, a concrete composition includesbatched concrete dry materials or wet batched concrete materials. System200 uses compressed air, water and a polymer-based solution composition(“polymer-based solution”) to provide a polymer-based solution foam thatis added in predetermined amounts to concrete in order to entrain air inthe concrete. Suitable polymer-based solution compositions for producingair-entraining foams are disclosed in U.S. Pat. No. 6,153,005 issuedNov. 28, 2000, to Welker, et al., the disclosure of which isincorporated herein by reference for all purposes. In the case of a drybatch plant, the foam may be discharged into truck 20 with or after thedry components have been loaded into the truck. In the case of a wetbatch plant, the foam may be mixed with the concrete prior to theconcrete being discharged into truck 20 or with the concrete as it isdischarged into the truck. In other cases, system 200 may be remote frombatch plant 10 in which case trucks 20 drive to the remote locationwhere the foam is discharged into the trucks. In yet other applications,system 200 may be located at the job site such that foam may be mixedwith concrete used at the work site such as drilling field.

It should be understood that, from the standpoint of an overall batchprocessing system for receiving an input product, mixing that productand providing the output product with, the above-disclosed system is arather small batch process. In order to ensure the consistency of such aprocess, it is important to ensure that all of the constituents that areplaced into the drum 18 are in such a state that they will mixcorrectly. For dry material such as cement sand and stone, this isrelatively easy as they have a “static” state. However, the foampresents a different issue. It is necessary for the foam to be correctlymixed by the system 200 for the given batch. The reason that thispresents an issue is that the foam requires multiple constituents andchemicals to be mixed in a very precise manner to achieve the correctconsistency of the foam, etc. For small batches, the system is typicallystarted up and the expectation is that the foam is produced in thecorrect mixture, etc. It is not possible to start the system up, run theprocess, determine if the consistency is right and then add it to thedrum 18. It is desirable that the system starts up and produces thecorrect consistency, etc., for the mixture at the beginning of the startof the batch and at the end thereof. If the system were a continuesrunning system, it would be possible to recalibrate the system as it isrunning, analyze the output and the various set points of all of thesub-processes that are employed in the overall process. It is difficultto provide feedback in realtime with a batch processing system that cananalyze the properties of the resulting product and then make adetermination as to what change must be made in order to correct forsome deviation of the output product from a desired range. Thus, it isnecessary to “fix” the process and control the sub-processes that makeup the overall process rather highly, as will be described hereinbelow.

FIG. 2 is a schematic representation of one variation of a system 200for producing a polymer-based solution foam, also referred to as anair-entrained foam, to entrain air into concrete further deployeddownhole. System 200 is controlled with a local system controller 202which, in one embodiment, may be a programmable logic controller (PLC).In other embodiments, local system controller 202 may be amicroprocessor provided with appropriate software and firmware.

In one variation, system 200 utilizes an air compressor 204 forproviding compressed air to produce the polymer-based solution foam.Compressed air from compressor 204 is controlled by local systemcontroller 202 to produce compressed air on demand. Compressed air fromcompressor 204 is directed through air line 206 through a waterseparator 208, after which the compressed air is directed through aparticulate filter 210 to remove any entrained particulates in the air.The compressed air is then directed to an air dryer 212 such as aregenerating desiccant type dryer or similar air dryer.

Compressed, filtered and dried air from dryer 212 is directed to apressure regulator 214 operating under the control of local systemcontroller 202. Pressure regulator 214 controls the pressure of the airmixed with water and the polymer-based solution to produce foam.Pressure regulated air from regulator 214 is directed through a valve216 that operates under the control of local system controller 202. Inone embodiment, valve 216 is a solenoid-type control valve that iseither in the open or closed position, depending upon whether foam isbeing produced at that point in time.

Water for the foam generation process is supplied from a process watersupply circuit generally designated as 215. Process water from thesupply circuit is directed through a filter 220. A water supply valve222 operating under the control of local system controller 202 is openedand closed to supply process water to a process water storage tank 226.A check valve 224 is provided to prevent any possible backflow. Processwater storage tank 226 is provided with a level indicator 228 and atemperature sensor 230. Local system controller 202 utilizes the signalfrom level indicator 228 to open and close water supply valve 222 basedupon three set points; a high level set point, a fill set point and alow level shut off set point. If the water level in process water tank226 drops below the fill set point, valve 222 is opened to supplyadditional water to the tank. If the water level in process water tank226 reaches the high level set point, valve 222 is closed. If the waterlevel in process water tank 226 falls below a predetermined low levelshut off set point, system 200 will be shut down or alternatively willnot be allowed to start up until sufficient water is added to processwater tank 226.

The temperature of process water used to produce foam is controlled witha closed loop circulating system designated 235. A temperature sensor230 is used to determine if the temperature of process water stored inprocess water tank 226 is at or within an acceptable range around thetemperature set point for the water temperature. The output from sensor230 is used by local system controller 202 to start or stop acirculating pump 236 and to energize a water heater 238. Circulatingpump 236 circulates water from process water supply tank 226 throughheater 238. A flow switch or flow meter 234 is used to ensure that theprocess water is being circulated through recirculating line 233, pump236 and heater 238 before the heater is energized under the control oflocal system controller 202. In some embodiments, a water cooler orrefrigeration unit (not shown) may be used in place of, or inconjunction with water heater 238 to cool process as necessary tocontrol the temperature of the water.

Temperature controlled process water from tank 226 is supplied through amanual outlet valve 232 to a process water supply pump 240. In oneembodiment, process water supply pump 240 is a vane-type, positivedisplacement pump driven with a variable speed drive 242 controlled bylocal system controller 202. Other metering pumps may be suitable. Localsystem controller 202 uses a signal from a flow meter 244 located downstream from supply pump 240 to increase or decrease the speed ofvariable speed drive 242 to increase or decrease water flow based on apredetermined set point. Process water pumped by pump 240 through flowmeter 244 is directed to a process water three way valve 248. In itsnormal operating position, process water three way valve 248recirculates process water back to process water supply tank 226 untilsuch time as system 200 is activated to produce foam. When system 200 isactivated to produce foam, valve 248 is repositioned to direct processwater through a check valve 250 to a mixing point 274 where the processwater mixes with a polymer-based solution. When system 200 is shut down,valve 248 is moved to the closed position.

Concentrated bulk aqueous-based solution for use in system 200 may bestored in a bulk storage tank 252, the level of which is monitored bylocal system controller 202 with a level sensor 253. In one embodiment,polymer-based solution from bulk storage tank 252 is pumped to apolymer-based solution batch tank 260 using a bulk polymer-basedsolution pump 256 operating under the control of local system controller202. Polymer-based solution batch tank 260 is part of a polymer-basedsolution supply circuit 261 used to supply polymer-based solution to apolymer-based solution circulating loop 263. Local system controller 202uses a signal from a level indicator 258 in polymer-based solution batchtank 260 to determine the volume of polymer-based solution in the batchtank and to add additional polymer-based solution to the batch tank asnecessary based on a preprogrammed set point.

From batch tank 260, polymer-based solution flows through a manualoutlet valve 262 to a polymer-based solution supply pump 264.Polymer-based solution supply pump 264 is typically a vane-type positivedisplacement pump powered by a variable speed drive 266. Local systemcontroller 202 uses a signal from flow meter 268, located down streamfrom polymer-based solution supply pump 264, to increase or decrease thespeed of variable speed drive 266 thereby increasing or decreasing theflow of polymer-based solution based on a preprogrammed set point. Thisallows the system to produce variable volumes (amounts) of air-entrainedcomposition of constant density and to account for the changes inhydrostatic pressure downhole. The polymer-based solution then flows toa three way polymer-based solution supply valve 270. Three waypolymer-based solution supply valve 270 may be positioned to recirculatepolymer-based solution back to polymer-based solution batch tank 260 orto direct the polymer-based solution through a check valve 272 to a teeor mixing point 274 where the polymer-based solution is mixed withprocess water.

The polymer-based solution and process water from tee 274 is directedthrough a mixing chamber 276 after which air is injected into thewater/polymer-based solution stream at a second tee or mixing point 278.The polymer-based solution/water/air mix is then directed into astationary mixer 280 to produce the polymer-based solution foam, whichin turn is deployed into the wellbore to set as a cement column having aconstant density or a varying density, if a single gas-to-base slurryratio is utilized. In one embodiment, stationary mixer 280 is packedwith a stainless steel or mesh or similar mesh to ensure adequate mixingof the polymer-based solution, water and air. It will be appreciatedthat one or more additional stationary mixers may be used down stream ofstationary mixer 280 to further condition the mixture to provide thedesired bubble size and consistency of foam.

As illustrated, a pressure sensor 282 is provided on foam discharge line283 down stream of stationary mixer 280 and before discharge point 289.The signal from pressure sensor 282 is input to local system controller202. The pressure measured by sensor 282 is compared to a preprogrammedvalue to determine whether system 200 is operating properly. If theinputs of one or more components, e.g., air, water or polymer-basedsolution, are interrupted or drift off of preprogrammed set points, thevariance will be reflected in the pressure measured by sensor 282. Forexample, if the polymer-based solution supply is interrupted, theviscosity of the mixture flowing through discharge line 283 will change,changing the pressure in the line. In this event, local systemcontroller 202 may be configured to shut down the process until thesource of the variation can be identified and corrected.

In one embodiment, the components of system 200, (with the exception ofair compressor 204, bulk storage tank 252 and water supply 218) may behoused in a single cabinet that may be transported to the drill site bymeans of a flatbed trailer that is positioned adjacent to the drillingapparatus and left onsite during well completion. In other variations,system 200 may be mounted directly on drilling platform. It will also beappreciated that the use of system 200 may allow for the use of fly ashin the base slurry thereby producing a slurry with more desirable flowproperties. System 200 may also be used to reduce the amount of Portlandcement used in the base slurry insofar as slurry having more consistentchemical and physical properties may be produced, especially in the casewherein fly ash is used as a component of the base slurry.

This configuration permits the system to be deployed rapidly andconveniently and/or moved from one location to another as needed. Inthis embodiment, the physical sub-processes, i.e., the water supplycircuit 215, the polymer solution supply circuit 262 and the compressair supply (regulator 214) are in close physical proximity (closelycoupled) such that no long pipe or tubing runs are required to connectthe sub-processes in the system.

Referring now to FIG. 2A, there is illustrated a simplified diagrammaticview of the general control system that operates in accordance with thatdescribed with respect to FIG. 2. In general, this control system iscomprised of a plurality of sub-controllers each controlling asub-process of the overall process. For example, one process involveswater circulation where water is continually circulated and maintainedat a constant flow rate and temperature. This requires a motor for apump to operate at a speed to produce the desired flow. When the processis control of the circulating pump for the polymer-based solution, whichkeeps the polymer-based solution circulating at a set flow rate, theprocess must be controlled to operate at a constant flow rate. It isimportant to note that, when this system starts up, all temperatures,pressures and the such are maintained at a “ready” status. Thus, thepressure with respect to the polymer-based solution is maintained withina defined set of constraints within the polymer-based solutioncirculating loop 263 such that, when valves 248, 270 are opened,polymer-based solution and water are delivered at the correct pressureand flow rate. This ensures that mixing occurs at the right temperatureand flow rate without requiring adjustments after mixing has begun.

Further, with respect to FIG. 2A, there is illustrated a plurality ofsub-processes 284. Each of these processes 284 is illustrated asreceiving some type of input and providing an output, one of theseprocesses being, for example, a motor controller for a circulating pump.This would require the pump to receive some type of control signal on aline 285, which would determine the speed of the motor. As an input, themotor would have a load placed on it and it also would operate in acertain environment, this being an external input parameter. If theprocess is water temperature control, then the input would be heat andthe process would be basically a heater to heat up the water. Therewould also be a flow control associated with the water. Each of theprocesses 284 would have associated therewith some type of sensor 286 tosense the associated measureable parameters. The sensor 286 wouldprovide information back to a control group sub-controller 288 on a line287. Each of the sub-controllers 288 comprises a sub-controllerassociated with the respective process for providing a control signalback on line 285. For a motor, the sensor would be the speed sensor andfor the temperature process, this would be at a temperature sensor. Forthe motor, the control would be a speed control whereas for thetemperature process, it would be a rheostat setting, for example.

Each of the sub-controllers 288 has set points associated therewith suchas speed, for the motor control sub-process, temperature for thetemperature sub-process, etc. These are self-contained loops that areonly associated with that particular sub-process. However, all thesub-processes together will form one large process. However, there is nofeedback from the output back to a system controller 290, which providesthe set points for the sub-controllers 288. Thus, without such feedback,it is difficult for the temperature controller for the water, forexample, to be integrated with the speed of any one of the motors tocontrol the overall output. It is not that the output could not beanalyzed and an output provided, but, rather, that in realtime this isnot feasible. Therefore, each of the sub-controllers 288 for thesub-processes 284 in the overall process would be operating withindefined constraints, this provided by the system controller 290operating in conjunction with the associated sub-controllers 288.

On start up, as set forth hereinabove, some of the sub-processes 284,operate to maintain temperatures, pressures, etc. For example, a volumeof water is continually circulated to maintain the temperature at acertain point and within a certain range. Further, the circulation pump236 (FIG. 2) is running such that it does not have to come up to speedso that there is no lag associated therewith. Therefore, when the systemis switched over to actually provide an output, i.e., mix theconstituents together, the water is at the correct temperature, themotor is at the right flow rate, the polymer-based solution is at theright pressure and flow rate, etc. Since the connections therebetweenare very short, this mixing is achieved very quickly at the “static”level set by the various set points in each of the sub-processes 284.Again, there is no interrelationship between the sub-processes 284 suchthat they are not part of an overall control loop. Each of thesub-control loops 288 is local to a particular sub-process 284. When thesystem is set up, all of the set points for the various sub-processes284 are tightly constrained and, once constrained, they are maintainedwithin these constraints by the system controller 290. As long as theseconstraints are maintained, the output will have consistent properties.Of course, if one of the sub-processes 284 fails, there are sensors 286that will indicate such, as described hereinabove.

FIG. 3A is a diagrammatic representation of system 200 of FIGS. 1 and 2.As illustrated, local system controller 202 includes one or morecommunications interface(s) 340 for communication with a variety ofinstruments and controls. In one embodiment, a batch ID number 300 and afoam volume request 302 are input to local system controller 202 by thebatch operator using a graphical user interface or similar device 346which communicates with local system controller 202 via a communicationsinterface 342. In other embodiments, different means or devices may beused to input the batch ID and the volume request to local systemcontroller 202. For example, in the case of a batch plant controlled bya computer or processor 355, the batch ID number 300 and a foam volumerequest 302 may be automatically transmitted to controller 202 via acommunications interface 353 upon receipt of an order or scheduling of abatch run.

Local system controller 202 receives a variety of instrument and controlinputs to control the operation of system 200. Inputs to local systemcontroller 202 may include the polymer-based solution level 304 inpolymer-based solution batch tank 260 (FIG. 2), the water level 306 inprocess water storage tank 226, and the water temperature 308 of thewater in the tank. Additional process parameters input to local systemcontroller 202 may include process air pressure 310 as measured atpressure regulator 214 (FIG. 2), the position 312 of air valve 216 andthe position 314 of water supply valve 218. In order to control theoperation of process water heater 238, local system controller 202receives an input 316 from a flow meter indicating whether water isflowing through the heater along with an input 318 indicating the statusof circulating pump 236 that directs water through the heater.

In order to control the operation of process water supply pump 240,local system controller 202 receives an input 322 from water flow meter244 which is used to control the speed 320 of variable speed drive 242of process water supply pump 240. Local system controller 202 alsoreceives an input 324 indicating the position of three way waterrecirculating valve 248. In connection with the supply of polymer-basedsolution to system 200, controller 202 receives an input 326 from alevel sensor 253 indicating the level of polymer-based solution in bulkstorage tank 253, an input 330 from level indicator 258 indicating thelevel of polymer-based solution in batch tank 260, and an input 332indicating the speed of polymer-based solution feed pump 256 and/or thespeed of the motor driving the pump. As previously noted, polymer-basedsolution feed pump 256 supplies polymer-based solution to polymer-basedsolution batch tank 260 under the control of local system controller202.

To control the flow of polymer-based solution to the process, localsystem controller 202 receives an input 334 from polymer-based solutionflow meter 268 and from variable speed drive 266 which drivespolymer-based solution supply pump 264. Local system controller 202 alsoreceives an input 336 from three way chemical recirculating valve 248indicating whether the valve is closed, in a position to recirculatepolymer-based solution back to polymer-based solution batch tank 260 orto direct polymer-based solution to mixing point 274 where thepolymer-based solution is mixed with process water. In order to monitorthe overall operation of the system 200, controller 202 receives aninput 338 from a pressure sensor 282 located in the foam discharge line283. If the flow of water, air or polymer-based solution is interruptedor varies from a preprogrammed set point, the interruption or variationwill result in a change of pressure in discharge line 283.

A communications interface 342 enables local system controller 202 tocommunicate with a local display and operator control module 344 whichmay include a graphical user interface 346. Graphical user interface 346may be used by the batch operator to enter information such as a batchID, a requested volume or quantity of foam to be incorporated into abatch of concrete or to override the operation of local systemcontroller 202 and/or adjust operating parameters such as flows or motorspeeds to produce variable volumes (amounts) of air-entrained cement ofconstant density to account for hydrostatic changes in a wellbore. Inone embodiment, local system controller 202 includes a communicationsinterface 348 connecting the controller to a portable control unit 350.Portable control unit 350 may be used by a batch operator or, forexample, a semi-truck driver to initiate or stop operations of system200, to enter a batch ID number or a truck ID number. This feature maybe particularly useful in the case where system 200 is located remotefrom the concrete batch plant. Portable control unit 350 may alsoinclude a bar code scanner, RFID reader or similar device foridentifying trucks as the trucks are queued and/or loaded with concrete.

Local system controller 202 may also include a communications interface352 enabling the controller to communicate with a remote central office356. The communications link with the remote central office 356 could bemade through a public or private network such as the internet, adedicated WAN or through a dial up modem, which would be a much slowerdata link. In one embodiment, communications interface 352 is anEthernet module enabling communications between local system controller202 and remote central office 356 via a public or private network 354such as the internet.

Remote central office 356 may include a user interface 358 enablingrealtime monitoring of the operation of system 200 including operatingparameters such as temperatures, flows, pressures and valve positions.In one variation, user interface 358 may be a touch screen. In otherembodiments, user interface 358 may be a display and a keyboard or asimilar input device. Information such as batch IDs, volume requests,the date and time at which a batch was prepared, alarms and/or overridesby a local operator may be logged. Graphical user interface 358 may alsobe used to make adjustments to operating parameters such as pump motorspeeds or valve positions from the remote central office 356. Finally,any alarms triggered as a result of interruptions or variations from setpoint(s) in the process may be annunciated on graphical user interface358 and logged at the remote central office 356 on a data storage device357 for future reference.

FIG. 3B is a diagrammatic representation of the system of FIGS. 1 and 2,illustrating one configuration of control paths for the system. Asillustrated, local system controller 202 is provided with one or morecommunications interfaces 340 for transmitting control signals tocomponents of system 200. Local system controller 202 may send a controlsignal 362 to air pressure regulator 214 including a pressure set pointfor the air supplied to system 200. Local system controller 202 may alsocontrol the position of air supply valve 216 by means of a signal 364setting the position of the valve. In one embodiment, valve 216 is asolenoid operated valve which may be set to an open or closed position.

A signal 366 from local system controller 202 controls the position ofwater supply valve 222 based on the water level in process water tank226 as previously described. Control signals 368 and 370 control theoperation of water recirculating pump motor 236 and water heater 238. Aspreviously noted, water heater 238 is used to heat the process water inprocess water tank 226 to a predetermined desired temperature. A flowswitch on meter 234 (FIG. 2) is used to ensure that water is circulatingthrough water heater 238 before the heater is energized.

The flow rate of process water in system 200 is controlled by a signalor set point 372 transmitted from local system controller 202 tovariable speed drive 242 which drives process water supply pump 240. Thespeed at which process water supply pump 240 is driven may be adjustedbased on a signal from flow meter 244 to local system controller 202.Local system controller 202 also generates a control signal 374 tocontrol the position of the three way valve 248 which may be closed,positioned to recirculate water back to process water tank 226 or todirect process water through check valve 250 to mixing point 274 wherethe process water is mixed with polymer-based solution.

The flow of polymer-based solution in system 200 is also controlled bylocal system controller 202. Local system controller 202 uses a signalfrom level indicator 258 and polymer-based solution batch tank 260 toactuate bulk polymer-based solution pump 256 as necessary to maintainthe desired level of polymer-based solution in the batch tank.Polymer-based solution from batch tank 260 is supplied to the system bymeans of a polymer-based solution supply pump 264 which is driven by avariable speed drive 266 operating based on a control signal 378received from local system controller 202. Control signal 378 may beadjusted to increase or decrease the speed of polymer-based solutionsupply pump 264 based on a signal from polymer-based solution flow meter268 received by local system controller 202. Local system controller 202also controls the position of three way polymer-based solution supplyvalve 270 by means of a control signal 380. As previously noted,polymer-based solution supply valve 270 may be positioned in a closedposition, a recirculating position wherein polymer-based solution isrecycled back to polymer-based solution batch tank 260 or to directpolymer-based solution to mixing point 274 where the polymer-basedsolution mixes with water.

FIG. 4 is a flow chart illustrating an exemplary process using system200 of FIGS. 1 and 2 to provide polymer-based solution foam forentraining air into concrete for a downhole injection. The processbegins at step 400 and at step 402 a batch plant operator receives anorder for a batch of concrete. Typically, the order will specify aparticular type of concrete and/or the relative amounts of the differentmaterials used to batch concrete. For example, the order may specifyamounts of cement, fly ash, sand, rock and/or different additives suchas plasticizers and retarders. The request will also typically include aspecified volume of concrete required. At step 404 a batch ID may beassigned to the particular request and the batch ID along with thespecifications for the batch may be recorded or stored by the batchplant operator. At step 406 information regarding the batch may betransmitted to local system controller 202. The information transmittedto local system controller 202 will typically include the batch ID, thevolume of the batch (normally in cubic yards) and the volume of desiredentrained air for the batch. The information may also be transmitted toa remote central office 356 where the information is stored in adatabase 357. Normally, the desired volume of entrained air will bespecified in terms of a volume, e.g. cubic of air per yard of concreteor in terms of a percentage on a volume basis. The information may betransmitted to local system controller 202 via a data link between thecontroller and a batch control computer for the concrete batch plant.Alternatively, the information may be manually entered by the batchcontrol operator using graphical user interface 346 (FIG. 3).

At step 408 a check is made to determine whether the transmittedinformation includes an air volume request. If not, the process loopsback and the batch operator may be prompted to enter a volume requestfor the particular batch. In one embodiment, after the air volumerequest is received, the information for the batch may be transmitted toremote central office 356 at step 410. The information may include thebatch ID, the date and time and the requested volume of entrained airfor the batch. At step 412 the required run time to produce the volumeof foam necessary to produce the desired amount of entrained air for thebatch is calculated. For example, if the desired volume of entrained airis 2 cubic feet and the capacity of system 200 is 0.2 cubic feet persecond, the required run time to produce the 2 cubic feet would be 10seconds. The required run time to produce the requested volume and thesystem status are stored on local system controller 202 at step 414.

At step 416 the status of various system variables are determined. Forexample, the water level in process water tank 226, the polymer-basedsolution level in polymer-based solution batch tank 260, the temperatureof the process water and the air pressure may be checked againstpreprogrammed set points. Turning to steps 418 through 424, if any ofthe aforementioned parameters are out of range an alarm may beannunciated at step 426. The alarm may be annunciated via graphical userinterface 346 (FIG. 3) or an audio device associated therewith to alertthe batch plant operator to the out of range parameter.

In one embodiment, system 200 is disabled and the alarm is locallyrecorded and transmitted to remote central office 356 at step 428. Atstep 430, the batch plant operator may make a decision to override thealarm or to take corrective action at step 431. Alternatively, thecorrective action may be remotely initiated from remote central office356. For example, by starting or adjusting a pump or opening or closinga valve. If the batch plant operator elects to override the alarm, theoverride may be transmitted to remote central office 356 at step 434 andbe logged at step 436 after which the water and polymer-based solutionsupply pumps may be started at step 438. If the parameters checked insteps 418 through 424, e.g., water level, polymer-based solution level,water temperature and air pressure, are within preprogrammed ranges,local system controller 202 will automatically proceed to start thewater and chemical pumps at step 438. It will be understood that whenprocess water supply pump 240 and polymer-based solution supply pump 264are started, the corresponding three way valves 248 and 270 arepositioned to recirculate water and polymer-based solution back to theirrespective storage tanks.

In one embodiment, the required volumes of polymer-based solution andwater are determined in milliliters for the purpose of accuracy andprecise control. At step 440 if the required volume of process water andpolymer-based solution has not previously been converted to milliliters,the required volumes are converted to milliliters. Turning to step 444,if the required run time to produce the desired volume of foam has notpreviously been calculated in milliseconds, the required run time isconverted to milliseconds. In this embodiment, the flow rates of waterand polymer-based solution used by system 200 will be in units ofmilliliters/milliseconds.

Referring now to step 446, the required volume of foam, the required runtime to produce the required volume of foam, the date and time of therequest and the system statistics are stored. This information may bestored locally on a data storage device 345 (FIG. 3A) associated withlocal system controller 202 and/or transmitted to remote central office356 and stored on a data storage device 357 associated with the remotecentral office. At step 448 a start discharge signal may be received byor generated by local controller 202.

In one embodiment, local controller 202 initiates the start dischargecommand after a predetermined or preprogrammed time period, for examplefrom about 30 seconds to about 2 minutes, beginning when the water andpolymer-based solution supply pumps are started. The delay betweenstarting the water and supply pumps and the start discharge commandpermits local controller 202 to make any adjustments to polymer-basedsolution or process flow rates necessary to stabilize the flows at thedesired levels. In other embodiments, the start discharge command may beinitiated by the batch plant operator using graphical user interface 346or portable controller 350 after the preprogrammed time period beginningwhen the water and polymer-based solution supply pumps are started. Inthe event that the start discharge command is not received or initiatedwithin a preprogrammed period of time after the polymer-based solutionand water pumps have been started at step 450, a timer associated withthe water and chemical pumps may time out after which, the pumps arestopped at step 452 and the process loops back to step 414.

At step 454, three way valves 248 and 270 (FIG. 2) corresponding to theprocess water and polymer-based solution feeds are opened to thedischarge position. Air supply valve 216 is also opened. Polymer-basedsolution and water are mixed at tee 274, flow through mixing chamber 276and are mixed at tee 278. The mixed air, foam and polymer-based solutionare directed through a second stationary mixer 280 and dischargedthrough discharge line 283. If local system controller 202 detects thatwater supply valve 248 or polymer-based solution supply valve 270 arenot in the proper position at steps 456 and 466, e.g., open todischarge, an alarm will be annunciated at step 458. Similarly, if thedischarged foam pressure as measured by pressure sensor 282 deviatesfrom the preprogrammed range at step 468, an alarm will be annunciatedat step 458. The alarm may be annunciated locally and/or transmitted tothe remote central office 356 where the alarm is logged at step 460. Atstep 462, the batch plant operator may elect to override the alarmand/or take corrective action at step 464. If the batch plant operatorelects to override the alarm, the override may be transmitted to theremote central office 356 at step 465 where the override is logged.

After system 200 has operated for the calculated run time to produce thedesired amount of foam, the process will time out at step 470 and thewater and polymer-based solution pumps will be stopped at step 472.Polymer-based solution supply valve 270 and water supply valve 248 willbe closed or returned to the recirculating position. At step 474, airsupply valve 216 (FIG. 2) will be pulsed one or more times to providesufficient compressed air to purge discharge line 283 of any foamremaining in the line. At step 476, the volume of foam delivered, theelapsed time for delivery, the date and time of the delivery andselected system statistics may be stored locally and/or transmitted tothe remote central office 356 and logged at the remote central office.At step 478, the process is ended and system 200 is reset to prepare thenext batch of foam.

Referring now to FIG. 5, there is illustrated a simplified diagrammaticview of the process flow described and illustrated with respect to FIG.2A hereinabove. In this process flow, there are illustrated only twosub-processes 284. There are illustrated a sub-process A, referencenumeral 502 and a sub-process B, reference numeral 504. Each of thesesub-processes 502 and 504 are illustrated as having an input 506associated with sub-process 502 and an input 508 associated withsub-process 504. Each sub-process also has a respective output 510 forsub-process 502 and output 512 for sub-process 504. Each of thesub-processes 502 and 504 are controlled by a respective sub-processcontroller 514 and 516. The sub-process controller 514 has a controlinput 518 that controls sub-process 502 and a return path 520 forclosing the loop. Thus, the sub-process controller 514 will send controlsignals to sub-process 502 and receive sensory inputs or state inputsfrom the sub-process 502. As described hereinabove, this is aself-contained process wherein the sub-process controller 514 hasassociated therewith parameters that define the set points for thatsub-process 502. The control signals provided to sub-process 502 willcontrol the process to meet those set points. As described hereinabove,these set points could be motor speed, fluid pressure, temperature, etc.The sub-process controller 516 operates in a similar manner with acontrol input 522 and a return path 524.

Each of the sub-processes 502 and 504 are part of an entire overallprocess. When operating as an integrated process, a process output 526will be provided. However, as further described hereinabove, each of thesub-processes is tightly coupled to the overall process such that, eachis operating at its particular set points as defined by its associatedsub-process controller 514, 516, the overall process output 526 willoperate at an expected value. In addition to being tightly coupled froma process standpoint, each of the sub-processes 502 and 504 (keeping inmind that many processes could be involved and only two are illustratedfor exemplary purposes) are tightly coupled from a physical standpoint.Each of the sub-processes 502 and 504 operate in an integrated and anon-integrated mode. In the non-integrated mode, all of thesub-processes are physically decoupled from each other but continue torun in accordance with the operation defined therein by the associatedsub-process controllers. The goal is that, when switching from anon-integrated to an integrated mode, the delay for the output process526 to become “stabilized” is minimal. By running each of thesub-processes at the desired set points and controlled in accordancewith the sub-process controller in a non-integrated mode, by switchingto an integrated mode, they will “seamlessly” integrate together toprovide the expected output in a very short period of time.

In many embodiments, the present system is utilized in small batchprocessing. For example to add 6 percent air (volume basis) to a typical10 cubic yard truck load of concrete would require approximately 16.2cubic feet of foam. In some embodiments, a system 200 such asillustrated in FIG. 2, may produce this amount or batch of foam in avery short period, for example 15, 30 or 45 seconds depending upon onthe specific configuration of the system. This short batch time isdesirable from a throughput basis, for example when adding batches offoam to a series of truck loads of concrete in rapid succession.However, since the amount of air-entrained foam added impacts thestrength of the concrete product, such time-constrained, small batchprocessing requires that the system produce foam with the desiredcomposition and properties almost instantly when the batch is initiated.

Thus, in the case of time-constrained small batch processing asdescribed herein, it is important that, when the batch process isinitiated (when the sub-processes are integrated), that the output willimmediately be at a stabilized process level. This prevents the long andexpensive time lag between stabilizing an output processor if all of thesub-processes are started up in an integrated mode. To achieve this,each of the sub-processes must be stable in the non-integrated mode and,when switching to the integrated mode, they must be tightly coupled suchthat, from a physical standpoint, all of the processes integrate tocombine in a very seamless mode. For example, when fluid is to bedelivered from one process to another process, i.e., to a mixingchamber, for example, it is important that the fluid be deliveredthereto at a particular pressure and temperature. As long as fluidpressure is stable and the temperature is stable prior to switching froma non-integrated mode to an integrated mode, the expectation is that thefluid will be input to the mixing process at the appropriate fluidpressure and temperature. Additionally, in the mixing process, theremight be air that is provided at a certain temperature, pressure andhumidity level which, in the non-integrated mode, is stabilized prior toswitching to the integrated mode. Once both of these are switched, it isimportant that there be little or minimal lag in the fluid beingdelivered to the mixing chamber and, as such, the mechanical (valves,tubing, etc.) connections between the two sub-processes is minimized.

Returning to FIG. 5, there is illustrated two mixing valves 528 and 530.Mixing valve 528 is operable to receive the output 510 from sub-process502 and either divert it to a path 532 or to the output process path526. The valve 528 is controlled by the system controller 290. The valve530 is operable to receive the output 512 from sub-process 504 andeither divert it to a path 534 or to the output process path 526. Thisoutput process path 526 for a multiple process system could be anotherprocess wherein that process requires two inputs. However, forsimplicity purposes, this is illustrated as a two sub-process system.

The paths 532 and 534 represent a closed loop stable system operating ina non-integrated mode. This path could loop around back to thesub-process or it could divert to some type of reservoir. For example,if it were necessary to provide air to the process output 526 at aparticular pressure, temperature and humidity, the air could merely beexhausted to the outside as opposed to recirculating it. For a fluiddelivery mode, the fluid could merely be circulated from a holding tankthrough a particular conduit at a particular pressure and temperature.Once the pressure and temperature of the fluid were stabilized, thiswould represent a stable operation of that particular sub-process in anon-integrated mode.

The system controller 290 is operable to provide to each of thesub-process controllers 514 and 516 parameters for operation thereof andalso receive therefrom monitoring information, i.e., information as towhether the sub-process controller is in a stable mode, etc. Inactuality, the system controller 290 and the sub-process controllers 514and 516 are all part of a single overall controller, wherein theoperations therein are virtual operation. However, each of theseoperations is independent and the system controller 290 can controlthese processes to operate in an integrated mode and a non-integratedmode. As will be described hereinbelow, when switching from anon-integrated mode to an integrated mode, the parameters may changesuch that, in the non-integrated mode, there is one set of parametersfor pre-integration and, after entering into integrated mode ofoperation, wherein the total process is “blended,” an additional set ofparameters may be provided such that the parameters of a particularsub-process are changed, i.e., the pressure of the fluid isincrementally changed, the temperature is changed or the flow rate ischanged.

Again, by tightly coupling each of the sub-processes in the overallprocess both from a process standpoint and from a physical standpoint,the sub-process can be stabilized prior to initiating a batch mode and,when the batch mode is initiated, there will be a seamless transition toa stable process output such that small batches can be accommodated fora duration of time. Further, when switching from an integrated mode to anon-integrated mode, the sub-process can be maintained in a stableoperating condition such that switching from non-integrated tointegrated, i.e., going to the batch mode, can be switched back andforth multiple times.

Referring now to FIG. 6, there is illustrated a flow chart depicting theoperation of a particular sub-process in integrated and non-integratedmodes. The program is initiated at a start block 602 and then proceedsto a function block 604 wherein a particular sub-process is initiated,this being in the non-integrated mode. This is initiated by the systemcontroller 290, which basically uploads the parameters to thesub-process controller associated with a particular sub-process and thesub-process will “ramp up” to its operating points. This will allow theprocess to stabilize at its particular set point. It may be that theoperation from initialization to stabilized operation will require someramping of things such as motor speed, temperature, etc. The sub-processin the overall process will receive some type of integrate request fromthe system controller 290. This integrate request will normally not beserviced until the sub-process is stable. Therefore, the operation ofthe sub-process will operate independently of the overall integration ofthe process until an integrate request is received, as indicated by adecision block 606. However, in one embodiment, the integrate requestwill not be serviced by the overall system unless the particularsub-process is stable, as indicated by a decision block 608. All thesub-processes should be stable before an integrate request can beserviced. This integrate request could be the mere pressing of a batchinitiation by an operator. Of course, there will typically be statuslights or other indicators associated with all of the sub-processorswhich would indicate to the operator that the batch should not beinitiated. However, if the batch were initiated prior to the sub-processbeing stable, the batch may be delayed. Once the sub-process is stable,the program will flow to a function block 610 to upload integrateparameters. As noted hereinabove, it is possible that the parametersover the set point for the operation of a particular sub-process maychange between the non-integrated mode and the integrated mode. If so,new parameters or set points would be uploaded to a particularsub-process when switching to the integrated mode. Once these areuploaded, the program will flow to a function block 612 to integrate theprocesses, i.e., the valves 528 and 530 of FIG. 5 would be switched todivert the outputs 510 and 512 to the process output path 526. Theprogram will then flow to a decision block 614 to determine if the batchwere complete, i.e., usually determined by a timer or indicated by theoperator. Until the batch was complete, the program would loop backaround to the input of function block 612 and, after the batch iscomplete, the program will flow to an end block 616.

Referring now to FIG. 7, there is illustrated a flow chart depicting theoperation of the sub-process when changing from the non-integrated modeto the integrated mode. This is initiated at a block 702 and thenproceeds to a decision block 704 to determine if the sub-process hasbeen initiated, i.e., the sub-process has been started from anon-operating mode. When initiated, in response to a control signal sentby the system controller 290, the program then proceeds to a functionblock 706 to upload the parameters for operation in the non-integratedmode. As described hereinabove, it is possible for the non-integratedmode and the integrated mode for a particular sub-process operatingindependently to be different. Once the parameters have been uploadedfor the operation of the sub-processer controlled by the associatedsub-process controller, the program then flows to a function block 708to run the control loop. This control loop can merely provide set pointsand control outputs and run the process until the set points have beenmet and the process is stable or the start up routine could involve sometype of ramping, i.e., the set points are continually changed until theyreach a desired set of set points. This will continue until the processis stable, which is determined at a decision block 710. When stable, theprogram flows to a function block 712 to report back to the systemcontroller 290 that the sub-process is operating in the non-integratedmode in a stable condition, i.e., all temperatures, pressures, fluidflow rates, etc., are at the desired set points. The program then flowsto a decision block 714 to determine if the sub-process is to enter intothe integrated mode. For the most part, if the operation in theintegrated mode and the non-integrated mode are the same, thesub-process does not change from one mode to the other. However, thereare certain situations wherein the sub-process operation, i.e., the setpoints, will be different between the integrated mode and thenon-integrated mode.

Once the integrated mode has been initiated, i.e., the operator haschosen to start the batch process, the program will flow to a decisionblock 716 to determine if parameters are to be changed. If not, then thesystem will maintain the control loop operation, as indicated by thefunction block 708. However, if the parameters are to be changed for theintegrated mode, the program will flow along a “Y” path to a functionblock 720 in order to upload new parameters for the integrated mode. Asnoted hereinabove, this could be a situation wherein a mixing chamberwhich requires input from another sub-process during the integrated modeand input from a process that allows air to be entrained into themixture from the first process would be combined. It may be that thepressure of the air or the flow of the air be reduced initially when theprocess is integrated and increased to ensure that the overall processoutput is maintained at a particular level. Therefore, these parameterscould be provided to that sub-process.

Once the new parameters are uploaded, the program flows to a functionblock 722, similar to function block 708, to run the control loop andthen to a decision block 724 to determine if the integrate sub-processis complete, i.e., is the process after the change in parameters stablein that it has reached the desired end set points. At this point, theparameters are fixed, as indicated by function block 726 and then theprogram will flow to a decision block 730 in order to determine if thebatch has been terminated. At this point, the program will eithercontinue in the batch operation to run the control loop from block 722or, once the batch is terminated, then the parameters will be reset tothe pre-integrated set points at function block 706 and the control loopwill run with these parameters. It can be seen that, with this loop, thesub-process will continue to run even when the batch is terminated suchthat the batch can be started and stopped many times without waiting forthe sub-processes to “ramp up.”

It can be seen in the batch processing mode, that by tightly couplingthe independent processors together to operate the processes from anintegrated mode to a non-integrated mode and then tightly coupling thesub-processes from a physical standpoint, the sub-processes can beintegrated in a seamless manner. This requires such things as divertervalves to be very tightly coupled from one process to the other suchthat diverted flow from one process in a non-integrated mode can beimmediately changed to divert the flow from a non-integrated mode to anintegrated mode such that the fluid will flow to the second process withvery little lag time.

In one embodiment, the slurry may be produced in a continuous manner andpumped into the wellbore. In another variation, the slurry may beproduced in a batch operation and stored in a holding tank (not shown)and pumped into a wellbore on as needed basis. In either variation,system 200 (as described above) is used to produce a foam that isadmixed with the slurry in mixer 18 (FIG. 1). As described in detailabove, a cement slurry including the required components, additives anda consistent controlled volume of entrained air is produced. It will beappreciated that the cement slurry produced in this fashion willminimize shrinkage and water bleed that may occur as the slurry sets inposition in the bore. This in turn will prevent or minimize theformation of void spaces or channels between the casing and the wellborethereby preventing or reducing gas leakage between the casing and thebore after the slurry has set in position.

It will be appreciated by those skilled in the art having the benefit ofthis disclosure that this system, method and apparatus for entrainingair in concrete for downhole injection provides a means of entraining acontrolled amount of air into batched concrete. It should be understoodthat the drawings and detailed description herein are to be regarded inan illustrative rather than a restrictive manner, and are not intendedto be limiting to the particular forms and examples disclosed. On thecontrary, included are any further modifications, changes,rearrangements, substitutions, alternatives, design choices, andembodiments apparent to those of ordinary skill in the art, withoutdeparting from the spirit and scope hereof, as defined by the followingclaims. Thus, it is intended that the following claims be interpreted toembrace all such further modifications, changes, rearrangements,substitutions, alternatives, design choices, and embodiments.

What is claimed is:
 1. A system for making stable cement slurry fordownhole injection, comprising: a controller for controlling the system,the controller including one or more communications interfaces forcommunicating with system components and a data storage device forstoring predetermined process parameters; a process water supply circuitfor providing temperature controlled process water for producing anair-entrained foam, including: a process water supply tank having atemperature monitoring device and a level detecting device, thetemperature monitoring device and level detecting device providingsignals to the controller indicating the level of process water in thewater supply tank and the temperature of the process water in theprocess water supply tank; a closed loop circulating system forcontrolling the temperature of the water in the process water supplytank including a circulating pump, a water heater and/or a water cooler,the circulating pump pumping water from the process water supply tankthrough the water heater and/or water cooler and back to the processwater supply tank to control the temperature of the process water,wherein the controller receives a signal from the temperature monitoringdevice and energizes or de-energizes the circulating pump, water heaterand/or water cooler based upon a preprogrammed temperature set point; aprocess water circulating loop including a process water supply pumpthat pumps water from the process water supply tank through the processwater circulating loop and back to the process water supply tank, afirst variable speed drive for driving the pump and a flow meter fordetermining the flow rate of process water in the process watercirculating loop whereby the controller receives a signal from the flowmeter and controls the speed of the first variable speed drive basedupon a preprogrammed set point; a first valve in the process watercirculating loop, the first valve diverting process water from theprocess water circulating loop to produce foam under the control of thecontroller; an aqueous-based air entrainment solution supply circuit forproviding an aqueous-based air entrainment solution for producing anair-entrained foam, including: an aqueous-based air entrainment solutionbatch tank having an aqueous-based air entrainment solution leveldetecting device for monitoring the level of aqueous-based airentrainment solution in the batch tank; an aqueous-based air entrainmentsolution circulating loop including an aqueous-based air entrainmentsolution supply pump that pumps aqueous-based air-entrainment solutionfrom the aqueous-based air-entrainment solution batch tank through theaqueous-based air-entrainment solution circulating loop and back to theaqueous-based air-entrainment solution batch tank, a second variablespeed drive for driving the aqueous-based air-entrainment solutionsupply pump and an aqueous-based air entrainment solution flow meter fordetermining the flow rate of aqueous-based air-entrainment solution inthe aqueous-based air-entrainment solution circulating loop whereby thecontroller receives a signal from the aqueous-based air-entrainmentsolution flow meter to control the speed of the second variable speeddrive to control the flow rate of aqueous-based air-entrainment solutionin the aqueous-based air-entrainment solution circulating loop; a secondvalve in the aqueous-based air-entrainment solution circulating loop,the second valve diverting aqueous-based air-entrainment solution underthe control of the controller to produce air-entrained foam; acompressed air supply for supplying compressed air for producing anair-entrained foam, including: a pressure regulator operating under thecontrol of the controller for regulating the pressure of the compressedair; an air supply valve for providing a consistent volume of air underthe control of the controller to produce air-entrained foam; a mixingchamber, the mixing chamber receiving process water and aqueous-basedair-entrainment solution diverted by first and second valves,respectively, and wherein the process water and aqueous-basedair-entrainment solution are blended in the mixing chamber; a stationarymixer, the stationary mixer receiving process water, aqueous-basedair-entrainment solution and compressed air and mixing the processwater, aqueous-based air-entrainment solution and compressed air toproduce an air-entrained foam; and a discharge line, for discharging theair-entrained foam for mixing with a concrete composition to produceair-entrained concrete connected to a pump for pumping an air entrainedstable cement slurry into a wellbore.
 2. The system of claim 1 furthercomprising a pressure sensor in the discharge line, the pressure sensortransmitting a signal to the controller, whereby the controller isoperative to actuate an alarm when the signal from the pressure sensorindicates a variance in one of the flow of process water, the flow ofthe aqueous-based air-entrainment solution or a change in the pressureof the compressed air used to produce the air-entrained foam.
 3. Thesystem of claim 1, wherein the system includes a graphical userinterface and a communications interface between the controller and thegraphical user interface whereby the graphical user interface isoperable to display selected process parameters based upon signalsreceived by the controller.
 4. The system of claim 1 further comprisingan air compressor for supplying compressed air for producingair-entrained foam and, wherein the air compressor is energized andde-energized by control signals from the controller.
 5. The system ofclaim 1 wherein the controller is operable to receive a request for aspecified amount of air-entrained foam and calculate a system run timeto produce the specified volume.
 6. The system of claim 1 wherein thecontroller is operable to actuate the process water supply pump, actuatethe aqueous-based air-entrainment solution supply pump and circulateprocess water and aqueous-based air-entrainment solution through theprocess water circulating loop and aqueous-based air-entrainmentsolution supply circuit, respectively, for a predetermined period andthen actuate the first and second valves to divert process water andaqueous-based air-entrainment solution to produce air-entrained foam fora downhole injection.
 7. A method for making stable cement slurry fordownhole injection, which comprises the step of entraining air into acement slurry further comprising the steps of: circulating process waterin a process water supply circuit for a predetermined period, the supplyincluding: a process water supply tank having a temperature monitoringdevice and a level detecting device, the temperature monitoring deviceand level detecting device providing signals to a controller indicatingthe level of process water in the water supply tank and the temperatureof the process water in the process water supply circuit; a closed loopcirculating system for controlling the temperature of the water in theprocess water supply tank including a circulating pump and a waterheater, the circulating pump pumping water from the process water supplytank through the water heater and back to the process water supply tankto control the temperature of the process water, wherein the controllerreceives a signal from the temperature monitoring device and energizesor de-energizes the circulating pump and water heater based upon apreprogrammed temperature set point; a process water circulating loopincluding a process water supply pump that pumps water from the processwater supply tank through the process water circulating loop and back tothe process water supply tank, a first variable speed drive for drivingthe pump and a flow meter for determining the flow rate of process waterin the process water circulating loop whereby the controller receives asignal from the flow meter and controls the speed of the first variablespeed drive based upon a preprogrammed set point; circulatingaqueous-based air-entrainment solution in an aqueous-based airentrainment solution supply circuit during the predetermined period, theaqueous-based air-entrainment solution supply circuit including: anaqueous-based air entrainment solution batch tank having anaqueous-based air entrainment solution level detecting device formonitoring the level of aqueous-based air-entrainment solution in thebatch tank, the level detecting device transmitting signals to acontroller indicating the level of aqueous-based air-entrainmentsolution in the aqueous-based air-entrainment solution batch tank; anaqueous-based air entrainment solution circulating loop including anaqueous-based air entrainment solution supply pump that pumpsaqueous-based air-entrainment solution from the aqueous-basedair-entrainment solution batch tank through the aqueous-basedair-entrainment solution circulating loop and back to the aqueous-basedair-entrainment solution batch tank, a second variable speed drive fordriving the aqueous-based air-entrainment solution supply pump and anaqueous-based air entrainment solution flow meter for determining theflow rate of aqueous-based air-entrainment solution in the aqueous-basedair-entrainment solution circulating loop whereby the controllerreceives a signal from the aqueous-based air-entrainment solution flowmeter to control the speed of the second variable speed drive to controlthe flow rate of aqueous-based air-entrainment solution in theaqueous-based air-entrainment solution circulating loop; after thepredetermined period, actuating first and second valves in the processwater circulating loop and the aqueous-based air-entrainment solutioncirculating loop, respectively, to divert process water andaqueous-based air-entrainment solution to a mixing chamber for mixing;adding compressed air to the mixed process water and aqueous-basedair-entrainment solution; directing the process water, aqueous-basedair-entrainment solution and compressed air to a stationary mixer toproduce an air-entrained foam; directing the air-entrained foam to adischarge line; and discharging the air-entrained foam into a cementcomposition to produce a concrete composition including entrained air.8. The method of claim 7 further comprising monitoring the pressure inthe discharge line with a pressure sensing device that transmits asignal to the controller as the air-entrained foam is discharged;comparing the pressure in the discharge line to a predetermined valuewith the controller; and wherein the local controller takes apreprogrammed set action if the pressure in the discharge line variesfrom the predetermined value.
 9. The method of claim 8 wherein thepreprogrammed set action is annunciating an alarm.
 10. The method ofclaim 7 further comprising using a pulse of compressed air to clear thedischarge line after a predetermined volume of air-entrained foam hasbeen discharged.
 11. The method of claim 7 further comprising monitoringeach of: a) the flow of process water through the process watercirculating loop, b) the flow of aqueous-based air-entrainment solutionthrough the aqueous-based air-entrainment solution circulating loop, andc) compressed air to the mixed process water and aqueous-basedair-entrainment solution; and wherein the controller compares the valuesof a, b and c with preprogrammed ranges and actuates the first andsecond valves to divert process water and aqueous-based air-entrainmentsolution to a mixing chamber for mixing only if a, b and c are withinthe preprogrammed ranges.
 12. The method of claim 7 further comprisingmonitoring each of: a) the flow of process water through the processwater circulating loop, b) the flow of aqueous-based air-entrainmentsolution through the aqueous-based air-entrainment solution circulatingloop, and c) compressed air to the mixed process water and aqueous-basedair-entrainment; and wherein the controller compares the values of a, band c with preprogrammed ranges annunciates an alarm if one of a, b or cvaries from the respective preprogrammed ranges.
 13. The method of claim7 further comprising: receiving an order for a specified amount ofair-entrained foam for a batch of concrete with the controller whereinthe controller calculates a run time to produce the specified amount ofair-entrained foam; producing the specified amount of air-entrained foamunder the control of the local controller; and discharging the specifiedamount of air-entrained foam into the concrete batch.
 14. The method ofclaim 7 further comprising: using the air-entrained foam to make cementof varying density before it is pumped downhole; deploying the cementslurry of varying density into the wellbore to set as a cement columnhaving a constant density; and continuously repeating said making of thecement slurry until a desired amount of cement slurry for a wellborecasing has been satisfied
 15. A process for preparing stable cementslurry for downhole injection, comprising: circulating process water ina process water supply circuit for a predetermined period; monitoringthe flow rate of the process water in the water supply circuit with aflow meter and transmitting a flow rate signal to a controller;comparing the flow rate of the process water to a preprogrammed processwater flow rate range with the controller and transmitting a signal withthe controller to adjust the flow rate of the process water if the flowrate is outside of the preprogrammed process water flow rate range;monitoring the temperature of the process water with a temperaturesensor and transmitting the temperature to a controller; comparing theprocess water temperature to a preprogrammed process water temperaturerange and transmitting a signal with the controller to adjust thetemperature of the process water if the temperature of the process waterfalls below a preprogrammed process water temperature range; circulatingaqueous-based air-entrainment solution in an aqueous-based airentrainment solution supply circuit during the predetermined period;monitoring the flow rate of the aqueous-based air entrainment solutionin the aqueous-based air entrainment solution supply circuit with a flowmeter; comparing the flow rate of the aqueous-based air entrainmentsolution in the aqueous-based air entrainment solution supply circuit toa preprogrammed aqueous-based air entrainment solution flow rate rangewith the controller and transmitting a signal with the controller toadjust the flow rate of the aqueous-based air entrainment solution ifthe aqueous-based air entrainment solution flow rate is outside of thepreprogrammed aqueous-based air entrainment solution flow rate range;monitoring the pressure of a compressed air supply with a pressuresensor and transmitting the pressure to the controller; comparing thepressure of the compressed air supply to a preprogrammed air pressurerange with the controller; after the predetermined period, if theprocess water flow rate is within the preprogrammed process water flowrate and the process water temperature is within the preprogrammedprocess water temperature range and the aqueous-based air entrainmentsolution flow rate is within the preprogrammed aqueous-based airentrainment solution flow range, (i) diverting process water from thewater supply circuit to a first mixer and (ii) substantiallysimultaneously diverting aqueous-based air entrainment solution from theaqueous-based air entrainment solution supply circuit to the firstmixer; adding compressed air to the mixed process water andaqueous-based air entrainment solution to produce an air-entrained foam;directing the air-entrained foam to a discharge line; discharging theair-entrained foam into a cement composition to produce a concretecomposition including entrained air; and pumping the concretecomposition including entrained air from the mixer into the wellbore.16. The process of claim 15 further comprising directing the processwater, aqueous-based air entrainment solution and compressed air to asecond mixer to produce an air-entrained foam;
 17. The process of claim15 further comprising: receiving an order for a specified amount ofair-entrained foam for a batch of concrete with the controller whereinthe controller calculates a run time to produce the specified amount ofair-entrained foam; producing the specified amount of air-entrained foamunder the control of the controller; and discharging the specifiedamount of air-entrained foam into the concrete batch.
 18. The process ofclaim 17 further comprising: monitoring the pressure in the dischargeline as the air-entrained foam is discharged with a pressure sensingdevice and transmitting a pressure signal to the controller as theair-entrained foam is discharged; comparing the pressure in thedischarge line to a preprogrammed value with the controller; and whereinthe controller takes a preprogrammed set action if the pressure in thedischarge line varies from the preprogrammed range.
 19. The process ofclaim 18, wherein the preprogrammed set action is annunciating a localalarm.
 20. The process of claim 18, wherein the preprogrammed set actionis transmitting a signal to a remote central office indicating that thepressure in the discharge line has varied from the preprogrammed range.21. The process of claim 15 further comprising supplying a pulse ofcompressed air to clear the discharge line after the specified amount ofair-entrained foam has been discharged.
 22. A method for preparingstable cement slurry for downhole injection in a small batch processing,comprising the steps of: operating a plurality of sub-processes in anintegrated mode and a non-integrated mode, each of the sub processesoperating independently in each of the modes to receive an input,process the input in accordance with an associated sub-process toprovide an output therefrom; integrating the outputs of thesub-processes in the integrated mode to physically interface each of thesub-processes in a batch process wherein each of the plurality ofsub-processes continues to operate independent of each other but withthe outputs thereof integrated into the batch process; and each of thesub-processes tightly coupled to the operation of the batch process andhaving a tight physical coupling thereto such that, when changed fromthe non-integrated mode to the integrated mode and the outputs thereofintegrated into the batch process, minimal delay occurs before the batchprocess is stabilized.
 23. The method of claim 22, wherein each of thesub-processes has an associated controller and a set of set points forthe operation thereof wherein the controller controls the sub-processesin accordance with the set points to provide a closed loop controlsystem that operates independently for each of the sub-processes. 24.The method of claim 22, wherein the set points are different from theintegrated mode to the non-integrated mode.
 25. The method of claim 22,wherein at least one of the sub-processes comprises the input foranother of the sub-processes.
 26. A cemented wellbore, which comprises:a cement composition, further comprising an air-entrained foam producedaccording to method of claim 7.